|4th 'Abbasid Caliph|
|Name||Musa b. Mahdi b. Mansur|
|Teknonym||Abu Ja'far or Abu Muhammad|
|Contemporary with||Imam al-Kazim (a)|
|Activities||Suppression of the Uprising of Fakhkh|
Mūsā b. Mahdi b. Manṣūr titled as al-Hādi al-'Abbāsi (b. 145/762 - d. 170/786) was the fourth Abbasid caliph. Al-Hadi al-'Abbasi ruled about 14 months. During his rule, 'Alids were under surveillance and their allowances were cut. During the rule of al-Hadi al-'Abbasi, Sahib Fakhkh made an uprising in Medina which was suppressed by him. He considered Imam al-Kazim (a) the main cause of provoking 'Alids in the Uprising of Fakhkh; and thus, he decided to kill Imam al-Kazim (a), but he died before committing that.
Al-Hadi al-'Abbasi wanted to appoint his small son (Ja'far) as the crown prince instead of Harun al-Rashid, but he could not. He followed the policy of his father, al-Mahdi al-'Abbasi in standing against Zindiqs (non believers) and killed many of them. After him, his brother Harun al-Rashid acceded to caliphate.